#define _CRT_SECURE_NO_WARNINGS 1
# include<stdio.h>
# include<math.h>
int main()
{
    /*********begin*********/
    float x1, x2, y1, y2, a;
    scanf("%f%f%f%f", &x1, &y1, &x2, &y2);
    a = sqrt((x1 - x2) * (x1 - x2) + (y1 - y2) * (y1 - y2));
    printf("%.2f", a);


    /*********end*********/
    return 0;
}